Chain Barrel in Loam. 6 5
In the propeller which we moulded in our last chapter
(Fig. 35) a screw template was placed outside the mould. There
are?cases, however, when a screw is to be moulded in loam, but
where the course mentioned cannot, for certain reasons, be
followed. Such is shewn at Fig. 73^.
A Chain Barrel for a crane is formed with a helical groove
to receive the chain. A is the casting required; B shews the
striking out of the loam, and c the finished mould. The only
portion requiring explanation is the screw </, made of hardwood.
It is fixed to the bottom plate, and has the same pitch as the
chain groove, though, of course, a more abrupt rise (for this
reasc>n made as large as convenient). The striking board runs on
the screw, being supported by a roller, and balanced by weight, as
in the case of the propeller.